Emulsion polymerization of butadiene-1,3 hydrocarbons



. of the films when the concentration of the emul- Patented May 1, 1945 2,375,140

UNITED STATES. PATENT OFFICE EMULSION POLYMERIZATION OF BUTADIEN E -1,3 HYDROCARBONS Waldo L. Semon, Silver Lake, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York ,No Drawing. Application July 21, 1942,

Serial N 0. 451,758

12 Claims. (Cl. 260-32) This invention relates to the emulsion polytadiene-1,3 hydrocarbons may be effected rapidly merization of butadiene-1,3 hydrocarbons and to produce synthetic latices which may contain particularly to an improved class of emulsifying even as high as 50% by weight of synthetic rubasents f r us in such p ym r at nsher and which may be used in the same manner It is known that synthetic rubber latices which as natural latex for the deposition of films and may be coagulated to yield synthetic rubber may the like, by employing as the emulsifying agent a be prepared by the polymerization in aqueous water soluble salt of an aliphatic-substituted benemulsion of butadiene-1,3 hydrocarbons either zene sulfonic acid wherein the aliphatic portion alone or in admixture with each other or with of the compound contains from 3 to 18 carbon other polymerizable compounds. In this process atoms. the formation of the aqueous emulsion containing The preferred emulsifying agents of this class the polymerizable materials, or monomers, necesare alkali metal salts of alkylated benzene sul-- sitates the use of an emulsifying agent and, for ionic acids wherein the total number of carbon this purpose, water soluble salts of fatty acids, atoms in the alkyl portion of the compound is or soaps, salts of sulfonated aliphatic compounds, 16 from 3 to 18, and still more preferably from 6 salts of alkylated naphthalene sulfonic acids and to 16, suitable examples of such compounds insalts of high molecular weight organic bases have eluding alkali metal mono-alkyl benezene sul-' heretofore been used. fonates wherein the alkyl group is propyl,

Such emulsifying agents, however, have not isopropyl, isobutyl, amyl, hexyl, octyl, nonyl, been entirely suitable especially in instances 20 decyl, undecyl, lauryl, tridecyl, myristyl, palmityl where it is desired to produce concentrated synor the like, preferably an alkyl group containing thetic latices which contain a relatively large profrom 6 to 16 carbon atoms; alkali metal dialkyl portion, say more than by weight, of synbenzene sulfonates wherein the alkyl group conthetic rubber and in instances where it is detains from 3 to 8 carbon atoms and the total sirable to employ the latex itself in the produc- 26 number of carbons in the alkyl groups is from tion of synthetic rubber articles in the same man- 6 to 16; alkali metal trialkyl benzene sulfonates ner that natural rubber latex is used. The prowherein each alkyl group contains from 3 to 5 duction of concentrated latices using the known carbon atoms and the total number of carbon emulsifying agents is not commercially feasible atoms in the alkyl groups is from 9 to 15; and because of the fact that relatively large amounts 50 other similar alkyl substituted benzene sulfonates. of emulsifying agent, about 5 to 15% of the weight However, other water soluble salts of aliphaticof the materials polymerized, and relatively large substituted benzene sulfonic acids wherein one amounts of water, about 200 to 500% of the or more other aliphatic substituents such as subweight of the materials polymerized, are necesstituted alkyl, alkylene, alkoxy, acyl, alkylamino, sary in order to form an emulsion which will dialkvlamino, alkylamide and other aliphatic remain fluid throughout the polymerization and groups are attached to thebenezene ring and the will enable the polymerization to be completed total number of carbon atoms in the aliphatic in a convenient interval of time, say less than portion of the compound is from 3 to 18, may also about 100 hours. Furthermore, the latices obbe employed. Moreover, either only one or more tained using ith r r l iv ly ar o small conthan one sulfonic acid or sulfonate radical may centrations of such known emulsifyin a ents are be attached to the benzene ring and the benzene not Suitable use ame i as ring may also be substituted by hydroxyl or car 3 latex, the deposltlon of thm -Y of boxy] groups'or other types of substituents but rubber for instance, because of the deleterious the latter are preferably not present efiect of the emulsifying agent on the properties These emulsifying agents may be prepared by known methods. For example alkali metal salts 1 1 l assess eassessassess: sf of may be dition of compounding ingredients or even upon muted by the sulfonatlon of alkylated zf mechanical agitation when the concentration of whlch may be prepared from alkyl halides and the l if in agent is relatively benzene by the Friedel-Crafts reaction. Other I have now discovered that the above-menaliphatic substituted benzene a es may tioned disadvantages attending the use of known Similarly be by the f nati n f the apemulsifying agents may substantially be elimiropriate benzene derivative or, in case the hated and that emulsion polymerizations of bul5 aliphatic substituent is an alkyl or dialkylamino I water soluble salts of aliphatic substituted benzene sulfonic acids are employed as emulsifying agents in the polymerization in aqueous emulsion of any of the butadiene-1,3 hydrocarbons including butadiene-i,3 itself, commonly termed butadiene, as well as its hydrocarbon homologs such' as isoprene, 2,3-dimethyl butadiene, piperylene and the like. Mixtures of such hydrocarbons with "one another or with one or more other monomers which are copolymerlzable therewith in aqueous emulsion to form linear copolymers may also be used. Such other monomers are, in general, readilv p lymerizable compounds containing an oleflnic group,

which is usually activated because of its presence atthe endofachainasinavinyl,

n CH|=&- or vinylidene CHFC group and/or because it is present in a conjugated system as in the structures etc. Examples of suitable monomers which are copolymerizable in aqueous emulsion with butadiene-l,3 hydrocarbons include aryl oleflns such as styrene, p-chloro-styrene, p-methoxy-styrene, vinyl naphthalene and the like; acrylic and substituted acrylic acids and their esters, nitriles and amides such as acrylic acid, methyl acrylate, ethyl 'acrylate, methyl alpha-chloro acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, ethacrylonitrile, methacrylamide and the like; methyl vinyl ether, methyl isopropenyl ketone, vinylidene chloride, vinyl furane, vinyl acetate, diethyl fumarate and the like. It is preferable, in'this invention, that monomer mixtures contain a larger amount of butadiene-L3 hydrocarbons than of other monomers, especially if the latex obtained by the emulsion polymerization is to be used as a substitute for natural rubber latex, but the invention is applicable to any mixture of butadiene-1,3 hydrocarbons and other monomers copolymerizable therewith in aqueous emulsion regardless of the proportions of the various constituents of the mixture.

Many methods and procedures for eiIecting the polymerization in aqueous emulsion of butadiene- 1,3 hydrocarbons or mixtures of monomers containlng the same are well known to the art and in general, these same methods and procedures may be employed when the emulsifying agents of this invention are utilized. Thus the polymerization may be carried out by agitating an emulsion containing the polymerizable material, water and emulsifying agent together, if desired, with various other substances which may be present, at a temperature of about 20 to C. for a time sufflcient for polymerization to occur, Obviously the time required for the polymerization will depend upon the nature of the particular emulsion; The polymerization of the emulsified monomers may be arrested, as by the addition to the emulsion of a polymerization inhibitor, after from about 70 to percent of the monomers have polymerized or it may be allowed to continue until substantially all of the monomeric material has been converted into polymer.

Substances which are preferably present in the emulsion during the polymerization, in addition to the monomers, water and emulsifying agent, include polymerization initiators which are usually necessary to effect the polymerization; polymerization catalysts or activators which are added primarily to speed up the process; polymerization modifiers which are added to increase the plasticity and solubility of the synthetic rubber product; and water-soluble salts which are added to prevent the formation of gels during the polymerization or to bring the emulsion to the pH,

most favorable for the action of the initiator. Exemplary initiators are hydrogen peroxide, potassium persuli'ate, sodium perborate, potassium percarborate, sodium periodate and other percompounds as well as diazoaminobenzene, dipotassium diazomethane disulfonate and the like. Exemplary catalysts or activators include simple and complex, water soluble, heavy metal salts such as ferric sulfate, cobaltous chloride and sodium cobaltinitrite; complex compounds consisting of heavy metal salts associated in complex formation with pyrophosphates, organic acids, certain sulfur-compounds such as beta-mercapto ethanol, sugars, sterols and the like; and other non-heavy metal containing catalysts such as certain vitamins, dicyan-diamidine-di-sulfate, and thiobarbituric acid. Exemplary modifiers include sulfur-containing organic compounds such as dialkyl dixanthogens, diaryl monoand di-sulfides, tetra alkyl thiuram monoand disulfldes, higher aliphatic mercaptans, and mercaptothiazoles. Salts which are added to prevent gel formation and/ or to regulate the pH of the emulsion include water soluble inorganic salts such as alkali metal chlorides, sulfates, phosphates, carbonates and borates and water soluble salts of organic acids such as alkali metal citrates, tartrates and oxalates. Obviously, many materials, pyrophosphates, persulfates, and carbonates, for examples, may serve dual or even tri le functions.

The preferred methods of practicing the invention and the improved results obtained when sion of butadiene-l,3 hydrocarbons may best be understood from the following specific examples which are intended to illustrate rather than limit the invention. The parts are by weight.

Example I An emulsion containing 55 parts of butadiene and 45 parts of acrylonitrile as the polymerizable materials, 5 parts of sodium diisobutyl benzene sulfonate as the emulsifying agent, 250 parts of water, 0.35 part of hydrogen peroxide as a polymerization initiator, 0.60 part of di-lsopropyl dixanthogen as a polymerization modifier, a catalyst mixture consisting of 0.60 part of sodium py-.

wet or dry. When the example is repeated ex-' cept that an equal quantity of di-isobutyl naphthalene sulfonate is employed as the emulsifying .agent, the polymerization requires over 100 hours for completion and the films deposited from the latex were cracked and opaque in appearance and were very weak both when wet or dry, Similar weak unsatisfactory films were obtained when the example was repeated using fatty acid soaps, and sodium alkyl sulfates asthe emulsifying agent. The latex prepared with the sodium diisobutyl benzene sulfonate as the emulsifying agent was also more suitable for dipping operations than the latex prepared with the other types of emulsifying agents.

Example II An emulsion similar to the emulsion described in Example I except that 2.1 parts of sodium tridecyl benzene sulfonate is employed as the emulsifying agent and only 210 parts of water are used, is prepared and is polymerized by agitating at 30 C. for 34 hours. The resulting latex contains about 45% by weight of a butadiene-acrylonitrile copolymer type synthetic rubber yet it is stable and does not coagulate on the addition of compounding ingredients such as zinc oxide. This latex may be used to deposit strong tough films or in dipping operations. Other latices prepared using equal amounts of soaps, hymolal sulfates and even alkylated naphthalene sulfonates as the emulsing agent are coagulated easily upon the addition of zinc oxide and in some cases even by mechanical agitation. Moreover, a much longer reaction time is necessary for the polymerization of similaremulsions prepared with these emulsifying agents than is required in this example.

Example III A mixture of 90 parts of butadiene, parts of piperylene and 90 parts of acrylonitrile is agitated at C. in the presence'of 1.8 parts of sodium lauryl benzene sulfonate dissolved in 180 parts of terials) of Naccanol NRSF, a commercially available emulsifying agent consisting of sodium salts of alkyl benzene sulfonic acids wherein the average chain length of the alkyl group is 12-14 carbon atoms. To the emulsion so obtained there is then added 0.27 part of di-isopropyl dixanthogen, 0.40. part of potassium persulfate, 0.30 part of N84P2O'1, 1.0 part of Na2HPO4, .015 part Of Fez(SO4)3.7H2O and .0015 parts of CoChfiHzO. and the emulsion is agitated at 40 C. for 41 /2 hours whereupon polymerization is complete. Although the latex contains over by weight of synthetic rubber it is fluid and quite stable and may be used to deposit excellent films, or in the manufacture of dipped goods or it may be coagulated to yield a high quality synthetic rubber. Similar results are obtained when the example is repeated using sodium nonyl benzene sulfonate, sodium myristyl benzene sulfonate, sodiu'm di-isopropyl benzene sulfonate and sodium palmityl benzene sulfonate as the emulsifying agent but another similar example using 'di-isopropyl naphthalene sulfonate required over 100 hours for polymerization and yielded an inferior latex.

Example V A mixture of 111 parts by weight of butadiene, 40 parts of styrene and 10.2 parts of alpha-methacrylamide is agitated untilpolymerization is complete at 40 C. in the presence of 210 parts of an aqueous solution containing 3.2 parts of sodium tridecyl benzene sulfonate as the emulsifyingagent, 0.35 part of hydrogen peroxide as an initiator, 0.72 part of di-isopropyl dixanthogen as a modifier and a small amount of a catalyst of the type used in the previous examples. The resulting latex is unusually stable and resists coagulation by mechanical means. The films obtained by drying the latex are unusually strong and tough.

As illustrated in the foregoing examples, the

amount of the emulsifying agent of this invention water as the emulsifying agent, 0.52 part of hydrogen peroxide, 1.2 parts of di-isopropyl dixanthogen and a small amount of a catalyst of the type employed in the previous examples. The latex obtained is quite stable and may be used to deposit films which exhibit excellent strength, elongation and elasticity.

Example IV which may be used in forming the emulsion, and still efiect a rapid polymerization, is somewhat smaller than may be employed with known emulsifying agents. However, larger amounts of emulsifying agent may also be employed, if

desired, without seriously affecting the properties of the films deposited from the latices. In general from about 0.5 to 5% of emulsifying agent based on the weight of the polymerizable materials gives excellent results, although larger or even smaller amounts may be employed. For this amount of emulsifying agent, amounts of water as small or even smaller than the amount of polymerizable materials may be used to prepare fluid emulsions, and consequently, it is possible to prepare latices containing from 30 to 50% or even higher of synthetic rubber when the emulsifying agents of this invention are employed. Obviously, this'permits the production of a larger quantity of synthetic rubber in a given amount of equipment than has heretofore been possible. However, if desired, more dilute latices may also be prepared using the method of this invention.

The synthetic rubber latices prepared by the method of this invention may be coagulated by the ordinary methods, such as by addition of acids or salts, to yield massive synthetic rubber which may then be used in the preparation of numerous articles, or the latices may be coagulated by electronic deposition processes employing electric currents or electrolytes in much the same manner as natural latex. Thus, these latices may be used in the manufacture of dipped goods etc. which have heretofore been made only from natural rubber latex.

Many modifications and variations which will the spirit and scope of the invention as defined in the appended claims.

sifying agent an alkali metal salt of an alkylated be apparent to those skilled in the art are within benzene sulfonic acid wherein the alnl portion of the compound contains from 3 to 18 carbon atoms. 3. In a process of polymerizing a mixture or a butadiene-1,3 hydrocarbon and at least one other compound containing an olefinic group, in an aqueous emulsion containing an emulsifying agent, the step which comprises using as the emulsifying agent an alkali metal salt of a mono-alkyl substituted benzene sulfonic acid wherein the alkyl group contains from 6 to 16 carbonv atoms.

,4. In a process of polymerizing a mixture of a butadiene-l,3 hydrocarbon and at least one other organic compound containing an oleflnic group,

in an aqueous emulsion containing an emulsifying agent, the step which comprises using as the emulsifying agent an alkali metal salt of a dialkyl substituted benzene sulfonic acid wherein the total number of carbon atoms in the alkyl groups is from 6 to 16.

,5. In a process of polymerizing a butadiene-L3 hydrocarbon in an aqueous emulsion containing an emulsifying agent, the step which comprises using as they emulsifying agent an alkali metal salt of a mono-alkyi substituted benzene sulfonic acid wherein the alkyl group contains from 6 to 16 carbon atoms.

6. In a process oi polymerizing a mixture including butadiene and acrylonitrile in an aqueous emulsion containing an emulsifying agent, the step which comprises using as the emulsifying agent an alkali metal salt or a di-alkyl substituted benzene suli'onic acid wherein the total number gcarbon atoms in the alkyl groups is from 6 to '1. In a process or polymerizing a mixture of butadiene and acrylonitrile in an aqueous emulsion containing an emulsifying agent, the step which comprises using as the emulsifying agent sodium di-isobutyl benzene sulfonate.

, 8. In a process of polymerizing a butadiene-L3 hydrocarbon in an aqueous emulsion containing an emulisiying agent, the step which comprises using as the emulsifying agent sodium lauryl ben-' zene sulfonate.

9. In a process of polymerizing a mixture of butadiene and styrene in an aqueous emulsion containing an emulsifying agent, the step which comprises using as the emulsifying agent sodium lauryl benzene sulfonate.

10. A synthetic rubber latex prepared by the polymerization of a butadiene-1,3 hydrocarbon in an aqueous emulsion containing a water soluble salt of an aliphatic-substituted benzene sulfonic acid wherein the aliphatic portion of the compound contains from 3 to 18 carbon atoms.

11. A synthetic rubber latex prepared by the polymerization of a mixture of a butadiene-1,3 hydrocarbon and at least one other compound containing an oleflnic group, in an aqueous emuls1on containing an alkali metal salt of a monoalkyl substituted benzene sulfonic acid wherein the alkyl group contains from 6 to 16 carbon atoms.

12. A synthetic rubber latex prepared by the polymerization of a mixture of a butadiene-L3 hydrocarbon and at least one other compound containing an olefinic group, in an aqueous emulsion containing an alkali metal salt of a di-alkyi substituted benzene sulfonic acid wherein the total number of carbon atoms in the alkyl groups is from 6 to 16.

WALDO L. SEMON. 

